Pregnancy Trimester Calculator
Find your current trimester, how many weeks until the next one begins, and the exact date range for all three trimesters.
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Pregnancy Trimester Result
-
Current TrimesterYour Trimester Timeline
| Weeks | Estimated Dates | |
|---|---|---|
| 1st Trimester | Weeks 1-13 | - |
| 2nd Trimester | Weeks 14-27 | - |
| 3rd Trimester | Weeks 28-40 | - |
Free Pregnancy Trimester Calculator
Use this free pregnancy trimester calculator to instantly find out which trimester you're currently in, how many weeks are left until the next one begins, and the exact estimated date range for all three trimesters of your pregnancy.
Unlike a simple week counter, this calculator lays out a full timeline of your pregnancy so you can see exactly when each trimester starts and ends, based on either your last menstrual period or your known due date.
How to Use the Pregnancy Trimester Calculator
- Choose whether you know your last menstrual period or your due date.
- Select the relevant date.
- Click Calculate My Trimester.
- View your current trimester, remaining weeks, and the full trimester timeline instantly.
Features
- Works from either your last menstrual period or a known due date.
- Shows exactly how many weeks and days remain in your current trimester.
- Lays out the estimated date range for all three trimesters, not just your current one.
- Mobile-friendly with print, share, copy, and download options.
Frequently Asked Questions
How are pregnancy trimesters divided?
Pregnancy is commonly divided into three trimesters: the first from week 1 to the end of week 13, the second from week 14 to the end of week 27, and the third from week 28 until birth.
How is my current trimester calculated?
This calculator counts your pregnancy from the first day of your last menstrual period, or works backward from your due date if that's what you entered, then matches your current week against the standard trimester ranges.
Why do the trimester dates matter?
Knowing your trimester dates can help you plan prenatal appointments, screenings, and milestones that are typically scheduled around specific trimester windows.
Is this calculator free?
Yes, this pregnancy trimester calculator is completely free to use with no sign-up required.
Method and Sources
This calculator counts pregnancy from the first day of the last menstrual period (LMP) and places each trimester using common boundaries: weeks 1–13, weeks 14–27, and week 28 until birth. If you enter a due date instead, it works backward 280 days to find the equivalent LMP.
Research that followed pregnancies with precisely measured ovulation dates found that natural pregnancy length can vary by as much as five weeks, even between healthy pregnancies. That is why any calculated date is an estimate, not a prediction of the exact day.
Trimester boundaries vary slightly between sources, and ultrasound dating may shift your timeline. Always follow the dates given by your doctor or midwife.
Sources:
- American College of Obstetricians and Gynecologists (ACOG) — Committee Opinion No. 700: Methods for Estimating the Due Date
- Jukic AM, Baird DD, Weinberg CR, et al. Length of human pregnancy and contributors to its natural variation. Human Reproduction, 2013
This calculator is for general information only and is not medical advice. Read our Calculation Methodology and medical disclaimer.
Related Calculators
Want to know your exact week rather than trimester? Try our pregnancy week calculator. Need to estimate your due date from scratch? Use the pregnancy due date calculator. Not sure when you conceived? Check the conception date calculator. Want a live countdown to your due date? Use the countdown timer. Curious about your baby's age after birth? See the baby age calculator.